Memory devices, such as random access memory (RAM), read-only memory (ROM), non-volatile memory (NVM) and like, are known in the art.
These devices provide an indication of the data which is stored therein by providing an output electrical signal. A device called a sense amplifier is used for detecting the signal and determining the logical content thereof. U.S. Pat. No. 4,916,671 to Ichiguchi describes one such sense amplifier.
In general, prior art sense amplifiers determine the logical value stored in a cell by comparing the output of the cell with a threshold voltage level. If the output is above the threshold, the cell is determined to be erased (with a logical value of 1) and if the output is below the threshold, the cell is determined to be programmed (with a logical value of 0).
The threshold level is typically set as a voltage level between the expected erased and programmed voltage levels which is high enough (or sufficiently far from both expected voltage levels) so that noise on the output will not cause false results. Typically, the expected erased and programmed voltage levels are 2.5V and 1.5V, respectively, and the threshold level is 2V.
Unfortunately, a high threshold level requires that the cell being sensed be given a sufficient amount of time to fully develop its signal thereby ensuring that, for an erased cell, the resultant signal has reached its full (high) voltage level. In order to achieve this in a reasonable amount of time, the entire array is first brought (or "equalized") to a medium voltage level which the cell being sensed either increases (if it is erased) or decreases (if it is programmed). The equalization operation is time-consuming and requires a considerable amount of power.